This is what I think : women like sex, no-really we do! And we like flirting and touching and feeling sexy. This girl is getting that from you. She doesn't NEED to sleep with you to get her needs met that are not being met by her boyfriend. Great for her, crapy for you. She is sublimating her desires for sex and cheating with this flirtatious sh*t. She may even be asking you on some level, if you are willing to be the other man/ cheat with her. She is not ready to let go of her boyfriend but she wants you to want her so she can gets these needs met. Which needs: the need to feel sexy, wanted, and cared for, to name a few. And you are doing this marvelously, you have played right into her hands. Why should she leave her boyfriend when she can get everything she needs from the BOTH of you ;) (To tell the truth you kind-of deserve it though, you knew she had a boyfriend, and troubles in the relationship and tried to exploit it. You may be made for each other.) Some women are like monkeys, they never let go of one branch without a firm grip on another. Meaning she may be shaping you for his replacement, and if it doesn't work out with you then she has not lost her boyfriend in the process. (Not all women are like this, but some are)
Also, just like not all women would seduce another man to meet their needs when their boyfriend can't (rather than breaking it like off, like a grown-up), so too, not all women say they like nice men and go after mean ones. Women like that have poor father figures, low self-esteem, and poor relationship role models. A pity.
Hope you are doing well, you asked for blunt right?